How to represent proportional control in a PID diagram
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As the title suggests, I am seeking guidance on how to implement proportional control in a PID system. For example: 1000 kg/hr of 98% sulfuric acid is diluted by adding water. The flow rates of sulfuric acid and water are measured using flow meters, and the two are mixed in a volume ratio of 1:2 to obtain sulfuric acid with a concentration of around 47%. A conductivity meter is then used to measure the concentration of the mixed sulfuric acid, and this value is used to fine-tune the aforementioned ratio. How can such a control scheme be represented in a PID system?
The representation of proportional control in a PID controller is as follows: 1. In a PID controller, proportional control is usually denoted by P. 2. In the control scheme, it is first necessary to measure the flow rates of sulfuric acid and water using flow meters respectively, and to feed these two flow signals into the input ports of the PID controller. 3. Next, these two flow signals need to be mixed in a 1:2 ratio, which can be achieved using a proportion calculator. The specific calculation formula is: sulfuric acid flow rate = total flow rate / (1 + 2). 4. Afterwards, a conductivity meter is used to measure the concentration of the sulfuric acid after mixing; this concentration signal is used as a feedback signal for the PID controller, and it is compared with the target concentration to determine the error signal. 5. Finally, the error signal is fed into the proportional control section of the PID controller, where it is amplified or reduced according to the proportional coefficient, thereby adjusting the sulfuric acid flow rate and controlling the concentration of the mixed sulfuric acid to reach the target concentration. When drawing a PID diagram, proportional control is usually represented by an arrow, with the arrow pointing to the final output, indicating the effect of proportional control on the output. The diagram also needs to indicate the names of components such as flow meters, ratio calculators, and conductivity meters, as well as the direction of their input and output signals. .
This is a cascade control system for sulfuric acid concentration and the sulfuric acid-to-water ratio. It is essentially a variable ratio control scheme. First, the flow rates of sulfuric acid and water are measured to form a dual closed-loop proportional control system ； The concentration of dilute sulfuric acid is measured to adjust the ratio of water to sulfuric acid. The system requires: two flow transmitters, one sulfuric acid concentration transmitter ； Two flow controllers, one sulfuric acid concentration controller ； Two control valves ； A multiplier (or divider).
Thank you! The main issue is that I don’t know how to draw it; I checked the technical manual but didn’t find any similar control schemes, or information on how the signals flow or how the controller functions. Could you recommend where I might find relevant information?